Navionics hot spot maps are good or even better is the app. Buy the $9.99 app for your smart phone and it will work like have an expensive locator in your boat. It will show all the contour lines plus will run off your GPS on your phone to show you where you are on the lake. A good preview of the app is to log on to the website. Google Navionics web app, click on the link and then zoom into the body of water you want to fish. THis is what you will see on your phone for mapping. I run the navionics lake chip in my boat and I will say its pretty accurate. Once you get up towards the river part, it varies as the river varies year to year. Give it a try. I gurantee you will like it plus it saves you hundreds from buying a GPS. If you dont want to do that, I agree with finding the channel and you will find fish.
I too struggle with Castle Rock in the aspect of bigger fish. I personally do very well in the spring time here but the ratio of little fish to keepers or slots is crazy. You can catch 100 little fish for every 15 inch fish. The crappie fishing seems to not have been what is has in the past. You will still catch a few here and there but limits are few and far between it seems. Good luck